Method for preparing ultra-loose sandstone sample and testing long-distance migration of particles

Abstract

The invention discloses a method for preparing an ultra-loose sandstone sample and testing long-distance migration of particles. The method comprises the following steps: freezing a rock core sample; arranging double-layer plugs at two ends of the core sample; sleeving a polyethylene thermal shrinkable sleeve outside the structure, and heating to obtain a washing oil sample; performing oil washing on the oil washing sample; drying the oil washing sample after oil washing, and arranging an elastic contractor at an injection end to obtain a displacement sample; displacing the displacement sample, collecting primary produced water at the extraction end until no particles are produced, and testing particle size distribution of the particles in the primary produced water; re-injecting the primary produced water into the displacement sample, collecting the secondary produced water at the extraction end until no particles are produced, and testing the particle size distribution of the particles in the secondary produced water after re-injection, so as to obtain the long-distance particle migration rule. The invention provides a new method with a better effect for researching the long-distance particle migration rule in the old oil field development process, and has important significance for economic and efficient development and utilization of oil reservoirs.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas field development research, and specifically relates to a method for preparing an ultra-loose sandstone sample and testing a particle long-distance migration. Background Art

[0002] The phenomenon of particle migration in oil and gas reservoirs is common in the process of oil and gas development and is considered to be an important reason for reservoir permeability damage and reduced oil and gas production capacity. Reservoir particles are sometimes dispersed in the intergranular pores in the form of fillers, sometimes not firmly cemented in a fixed position by natural cements in the rock, and sometimes even in the form of loose particles on the inner surface of the pore wall or skeleton particles. The damage mechanism of reservoir particle migration mainly includes surface deposition or adsorption, bridging or extrusion deformation at the pore throat, and agglomeration inside the pore. Under the action of pressure excitation or invasion of external fluids, reservoir particles fall off from the inner wall of the pore, and are retained and deposited when migrating to the pore throat position with the pore fluid, and then block the reservoir, which is one of the key factors causing reservoir damage and seriously affects oil and gas production capacity. Therefore, it is of great significance to establish an efficient and accurate experimental method for testing particle migration in loose sandstone reservoirs and accurately understand the damage law of particle migration to the reservoir to achieve efficient development and utilization of oil reservoirs.

[0003] In the field of loose sandstone sample processing, the commonly used methods include encapsulation processing methods such as glue coating method and metal sleeve method. Since the colloid can easily invade the sample gap and contaminate the sample, and is not resistant to solvent cleaning, it directly affects the pore structure of the sample. At present, in order to ensure the integrity of the core, several core preparation methods have been developed and studied, mainly by sealing the mined core. For example, Xu Jianjun et al. disclosed four sealing methods in "A Study on Sampling Method of Loose Sandstone Cores", namely, sealing with lead sleeves, sealing with polytetrafluoroethylene tape only, sealing with polytetrafluoroethylene tape and lead sleeves, and wax boiling consolidation to achieve wax sealing; for example, Li Haijiang et al. disclosed in "A Brief Discussion on Special Core Sample Preparation Technology" that loose sandstone can be prepared by liquid nitrogen freezing method, and the frozen rock samples can be encapsulated to prepare cores to ensure the integrity of the core during the experiment. The encapsulation is to first wrap the core with a liner such as polytetrafluoroethylene, then put on a permeable net, put on a pressure ring, put on a heat shrink tube, and bake it on an alcohol lamp until it is completely shrunk and tightened. None of the above methods consider the collapse of loose cores during oil washing, and cannot accurately test the impact of particle migration on reservoir cores. Summary of the invention

[0004] The present invention is proposed to solve the problems in the prior art that ultra-loose sandstone has poor cementation and the pore structure is easily deformed in the experiment. Its purpose is to provide a method for preparing ultra-loose sandstone samples and testing the long-distance migration of particles.

[0005] The present invention is achieved through the following technical solutions:

[0006] A method for preparing ultra-loose sandstone samples and testing long-distance particle migration comprises the following steps:

[0007] S1. Freeze the core samples at -15℃~-5℃;

[0008] S2, setting double-layer plugging at both ends of the core sample frozen in step S1;

[0009] S3, a polyethylene heat shrink sleeve is placed outside the structure obtained in step S2, and the polyethylene heat shrink sleeve is heated to shrink the polyethylene heat shrink sleeve to wrap the core sample and the double-layer plugging at both ends thereof, thereby obtaining a wash oil sample;

[0010] S4, placing the wash oil sample prepared in step S3 into a Soxhlet extractor for washing oil;

[0011] S5, drying the washed oil sample after washing the oil, and setting an elastic shrinkage device at the injection end of the washed oil sample after washing the oil to obtain a displacement sample;

[0012] S6, placing the displacement sample obtained in step S5 into a displacement device, displacing the displacement sample with configured formation water, collecting primary produced water at the production end until no more particles are produced, and testing the particle size distribution of the particles in the primary produced water;

[0013] S7. Re-inject the primary produced water collected in step S6 into the displacement sample, collect the secondary produced water at the production end, until no more particles are produced, and test the particle size distribution of the secondary produced water after reinjection, that is, obtain the long-distance particle migration law.

[0014] In the above technical solution, the diameter of the core sample in step S1 is 2.5 cm, and the core sample is an ultra-loose sandstone core sample drilled from a full-diameter core containing formation crude oil and maintaining the original pore structure.

[0015] In the above technical solution, the freezing treatment condition of step S1 is: freezing for 5h to 10h at a low temperature, so that the core sample is cylindrical in the frozen state.

[0016] In the above technical solution, the double-layer sealing includes an inner layer of non-magnetic fine yarn mesh and an outer layer of porous polyethylene gasket.

[0017] In the above technical solution, the inner layer of non-magnetic fine yarn mesh is 300-400 mesh, and the mesh diameter of the fine yarn mesh is equal to the median particle size of the core.

[0018] In the above technical solution, both ends of the polyethylene heat shrink sleeve sleeved on the outside of the structure obtained in step S2 in step S3 extend beyond the corresponding end portions of the structure obtained in step S2 by 2.5 cm to 3 cm.

[0019] In the above technical solution, the heating in step S3 is performed by blowing with a hot air gun, and the hot air gun blowing process ensures that the polyethylene heat shrink sleeve is evenly heated all around, so that the polyethylene heat shrink sleeve tightly wraps the core sample and the double-layer seals at both ends.

[0020] In the above technical solution, in step S4, the Soxhlet extractor uses kerosene as the washing oil medium, sets the temperature according to the shrinkage rate of the heat shrink sleeve, and uses a temperature control instrument to slowly heat.

[0021] The beneficial effects of the present invention are:

[0022] The present invention provides a method for preparing an ultra-loose sandstone sample and testing the long-distance migration of particles. Based on the ultra-loose sandstone sample, the invention takes into account factors such as poor cementation, loose structure and low strength of the ultra-loose sandstone, and designs the wrapping preparation of the core so that the core will not collapse and become shapeless due to the washing out of crude oil during the oil washing process. The method for the collapse of the core at the outlet end of the loose sandstone during the displacement process is optimized, and the particle test under the influence of the core collapse of the loose sandstone core during the long-term water drive process is eliminated, so that the study of the particle migration law is more accurate, and the method is applied in the high-precision particle migration law test experiment of the water drive oil reservoir, which is of great significance for the economic and efficient development and utilization of the oil reservoir. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a flow chart of the method of the present invention;

[0024] Figure 2 It is a schematic diagram comparing the method of the present invention with a conventional testing method.

[0025] For ordinary technicians in this field, other relevant drawings can be obtained based on the above drawings without any creative work. DETAILED DESCRIPTION

[0026] In order to enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention is further described below with reference to the accompanying drawings and through specific implementation methods.

[0027] Example 1

[0028] like Figure 1 As shown, a method for preparing ultra-loose sandstone samples and testing long-distance particle migration includes the following steps:

[0029] S1. Drilling core samples: Drilling ultra-loose sandstone core samples with a diameter of 2.5 cm containing formation crude oil and maintaining the original pore structure from full-diameter cores under liquid nitrogen freezing conditions; drilling rock samples under liquid nitrogen freezing conditions is to prevent the phenomenon of core collapse and shapelessness during the drilling process;

[0030] S2, freezing the core sample: freezing the core sample obtained in step S1 at a low temperature of -15°C to -5°C for 5h to 10h, so that the core sample is cylindrical in the frozen state;

[0031] S3, setting double-layer plugging at both ends of the core sample frozen in step S2;

[0032] The double-layer plugging comprises an inner layer of non-magnetic fine yarn mesh and an outer layer of porous polyethylene gasket.

[0033] The inner layer of non-magnetic fine yarn mesh has a mesh size of 300 to 400, and the mesh diameter of the fine yarn mesh is equal to the median diameter of the core particle size.

[0034] S4, a polyethylene heat shrink sleeve is placed outside the structure obtained in step S3, and the polyethylene heat shrink sleeve is heated to shrink the polyethylene heat shrink sleeve to wrap the core sample and the double-layer plugging at both ends thereof, thereby obtaining a wash oil sample;

[0035] The heating is carried out by blowing with a hot air gun, and the hot air gun blowing process ensures that the polyethylene heat shrink sleeve is evenly heated all around, so that the polyethylene heat shrink sleeve, the core sample, the fine gauze at both ends and the porous fixing sheet are tightly wrapped to obtain a shaped rock sample with self-cementing properties;

[0036] S5, placing the wash oil sample prepared in step S4 into a Soxhlet extractor for washing oil;

[0037] The tightly wrapped shaped rock sample prepared in step S5 is placed in an extractor, kerosene is used as an oil washing medium in the extractor, the temperature is set according to the shrinkage rate of the heat shrink sleeve, and the heat is slowly heated using a temperature control instrument. While the crude oil is washed out, the heat shrink sleeve is further shrunk by the heat, so that the rock particles are poorly cemented due to the washing out of the crude oil, and the core that is easy to deform and collapse is reshaped, thereby obtaining a core sample after oil washing;

[0038] S6, drying the washed oil sample after washing the oil, and setting an elastic shrinker at the injection end of the washed oil sample after washing the oil to obtain a displacement sample;

[0039] During the experiment, the elastic shrinkage device always provides an extrusion force to the core sample after oil washing, so that the porous fixing plate at the core outlet is close to the end surface of the core sample after oil washing, supporting the displacement sample to prevent collapse during the displacement process;

[0040] S7, placing the displacement sample obtained in step S6 into a displacement device, using the configured formation water to displace the displacement sample, collecting the primary produced water at the production end until no more particles are produced, and testing the particle size distribution of the particles in the primary produced water;

[0041] After washing and drying, displacement experiments were conducted. Due to the poor cementation, loose structure and low strength of ultra-loose sandstone, the displacement process is often accompanied by the shedding and migration of particles and the collapse of the outlet, and it is impossible to obtain accurate particle migration rules. The core was placed in the core holder for displacement experiments, and the particles in the outflow displacement were collected and monitored. The experiment was suspended when there were no particles in the outflow displacement.

[0042] S8. Re-inject the primary produced water collected in step S7 into the displacement sample, collect the secondary produced water at the production end, until no more particles are produced, and test the particle size distribution of the secondary produced water after reinjection, that is, obtain the long-distance particle migration law.

[0043] In step S8, the collected outflow water is reinjected into the core. At this time, the rock particles caused by collapse will stay in the cavity formed between the elastic shrinkage device at the inlet end and the experimental core, and the particles that migrated long distances inside the core will be eliminated again. The outflow water at this time is collected for testing to obtain accurate long-distance particle migration rules.

[0044] Through Table 1 and Figure 2 It can be seen that, by comparing the ultra-loose sandstone sample preparation and particle long-distance migration test method of the present invention with the conventional test method, the particle size detected by the method of the present invention is more precise, the result value is relatively accurate, and is not affected by core collapse; the conventional test method is affected by core collapse, and some larger particles are driven out, affecting the test result, and the result value is biased large.

[0045] Table 1: Comparison table between the method of the present invention and the conventional method

[0046]

[0047] The present invention specially designs the ultra-loose core into oil washing samples and displacement samples, and maintains its original pore structure to the greatest extent during the test process, so as to achieve accurate measurement of the size distribution of particles that migrate over long distances within the formation; the ultra-loose sandstone oil washing samples are prepared by means of the polytetrafluoroethylene heat shrinkage principle, so that the rock particles remain in place during the oil washing process; secondly, the oil washing samples are added with elastic shrinkers to prepare ultra-loose sandstone displacement samples, and the displacement samples are displaced using the configured formation water; finally, the particle size distribution of the particles in the primary produced water and the secondary produced water after reinjection is detected to determine the size of the particles that migrate over long distances. The present invention avoids the influence of the collapse and deformation of the ultra-loose core on the experimental results, which is conducive to the accurate optimization of development parameters of the oil field.

[0048] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing ultra-loose sandstone samples and testing long-distance particle migration, characterized in that: The following steps are involved: S1, frozen core samples; S2, setting double-layer plugging at both ends of the core sample frozen in step S1; S3, a polyethylene heat shrink sleeve is placed outside the structure obtained in step S2, and the polyethylene heat shrink sleeve is heated to shrink the polyethylene heat shrink sleeve to wrap the core sample and the double-layer plugging at both ends thereof, thereby obtaining a wash oil sample; S4, placing the wash oil sample prepared in step S3 into a Soxhlet extractor for washing oil; S5, drying the washed oil sample after washing the oil, and setting an elastic shrinkage device at the injection end of the washed oil sample after washing the oil to obtain a displacement sample; S6, placing the displacement sample obtained in step S5 into a displacement device, displacing the displacement sample with configured formation water, collecting primary produced water at the production end until no more particles are produced, and testing the particle size distribution of the particles in the primary produced water; S7. Re-inject the primary produced water collected in step S6 into the displacement sample, collect the secondary produced water at the production end, until no more particles are produced, and test the particle size distribution of the secondary produced water after reinjection, that is, obtain the long-distance particle migration law.

2. The method for preparing ultra-loose sandstone samples and testing long-distance particle migration according to claim 1 is characterized in that: The diameter of the core sample in step S1 is 2.5 cm. The core sample is an ultra-loose sandstone core sample drilled from a full-diameter core and containing formation crude oil and maintaining the original pore structure.

3. The method for preparing ultra-loose sandstone samples and testing long-distance particle migration according to claim 1 is characterized in that: The freezing treatment conditions in step S1 are: freezing at -15°C to -5°C for 5h to 10h, so that the core sample is cylindrical in the frozen state.

4. The method for preparing ultra-loose sandstone samples and testing long-distance particle migration according to claim 1 is characterized in that: The double-layer plugging comprises an inner layer of non-magnetic fine yarn mesh and an outer layer of porous polyethylene gasket.

5. The method for preparing ultra-loose sandstone samples and testing long-distance particle migration according to claim 4 is characterized in that: The inner layer of non-magnetic fine yarn mesh has a mesh size of 300 to 400, and the mesh diameter of the fine yarn mesh is equal to the median diameter of the core particle size.

6. The method for preparing ultra-loose sandstone samples and testing long-distance particle migration according to claim 1, characterized in that: Both ends of the polyethylene heat shrink sleeve sleeved on the outside of the structure obtained in step S2 in step S3 extend beyond the corresponding ends of the structure obtained in step S2 by 2.5 cm to 3 cm.

7. The method for preparing ultra-loose sandstone samples and testing long-distance particle migration according to claim 1 is characterized in that: In step S3, the heating is performed by blowing with a hot air gun, and the hot air gun blowing process ensures that the polyethylene heat shrink sleeve is evenly heated all around, so that the polyethylene heat shrink sleeve tightly wraps the core sample and the double-layer seals at both ends.

8. The method for preparing ultra-loose sandstone samples and testing long-distance particle migration according to claim 1 is characterized by: In step S4, the Soxhlet extractor uses kerosene as a washing oil medium, sets the temperature according to the shrinkage rate of the heat shrink sleeve, and slowly heats using a temperature control instrument.

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